Description

Knapp was born in Dauborn, Hessen-Nassau in 1832. He became a student of Helmholtz and an assistant of von Graefe. He moved to New York in 1868. He became professor of ophthalmology at the Medical College of the University of New York. He died in 1911.
Knapp developed a scope with two discs. He presented it at the meeting of the American Ophthalmological Society in Newport in July 1873.
A concave mirror is the reflector. There are two discs behind the mirror. The upper disc has an empty opening and convex lenses: 3,4,6,8,10,12,14,17,20,24,33,48. The lower disc has an empty opening and the same series of concave lenses. In 1874, the lenses +2 and -2 were added. The lenses are protected from dust by a thin removable metal plate.
The manufacturer was Miller Brothers, 1223 Broadway, New York. Its price was $40.00.